A spall liner is a type of armor typically attached to the inside hull of a vehicle such as a helicopter, aircraft, watercraft vessel, or ground vehicle. See U.S. Pat. Nos. 5,170,690 and 5,333,532 incorporated herein by this reference. The spall liner may include plies of Kevlar® or other similar ballistic protective material and may be assembled in panels tailored to match the inside configuration of the vehicle (for example, wall, door, floor, and ceiling panels).
As our military faces new weapons and threats, there is a need for very thick spall liners, for example, 37 or more plies of Kevlar® or even as thick as 50 or more plies of Kevlar®. Contrary to conventional wisdom, it has now been demonstrated that very thick spall liners are effective as armor for a number of different threats.
It is very difficult to secure that many plies of Kevlar® together. Modern sewing machines, for example, cannot sew more than about 10-12 or perhaps as many as 19 plies of Kevlar® depending on their thickness. If the numerous plies of Kevlar® in a thick spall liner are not secured together, its durability in the field is diminished. If the plies are too tightly sewed together, the ballistic effectiveness of the spall liner in the field is also diminished.